Combined principle of condensation and membrane separation: Process logic for two-stage treatment of oil and gas recovery

Oil and gas recovery devices are commonly connected in series with two stages of condensation and membrane separation. Many people ask why they can't leave only one stage. The reason is that the two stages have different mechanisms of action: condensation liquefies condensable components by cooling, which has the highest efficiency for high-concentration gas source, but due to the temperature limit of refrigerant, there is still residual vapor at the outlet; Membrane separation separates organic vapor from air by dissolution and diffusion difference, which is suitable for deep treatment of low concentration and atmospheric volume, but directly sends high-concentration gas source into membrane, with large load and short service life. The two-tiered combination allows each to leverage its strengths.

First stage condensation: liquefying the body

The logic of the condensation section is very simple: the gas is cooled by the heat exchange surface, the components with high boiling point are liquefied first, and the condensate is discharged for recovery. The key to the effect is the temperature level and the heat transfer area. The temperature level is determined according to the boiling point of the target component. The easily liquefied part is recovered with conventional frozen water first. Whether to continue to deepen the cold depends on the residual concentration and emission requirements. The efficiency of condensation decreases with the decrease of concentration, and the lower the concentration, the higher the marginal energy consumption of continuous recovery by cooling.

Three steps of condensing section design

1. Determine the condensing temperature level according to the gas source components, first conventional refrigerant and then deep cooling, and set it in stages;
2. Calculate the heat exchange area according to the gas volume and load, leaving the allowance of frosting condition;
3. Set up condensate separation and drainage, with low point drainage to avoid effusion.

Second stage membrane separation: intercepting residual vapors

The principle of the membrane separation section is that the dissolution and diffusion rate of organic vapor in the membrane material is much higher than that of air. When the mixed gas containing organic vapor passes through the membrane, the organic component preferentially passes through the membrane to become the enrichment side and is sent back to the condensation inlet to form an internal circulation, while the air side is discharged as purified gas. The performance of the membrane depends on selectivity and flux, and too high inlet concentration will cause membrane fouling and load concentration, which is why it needs to be placed after condensation.

Two-stage serial operation logic

1. The air source enters the condensation section by stabilizing the pressure of the buffer tank;
2. The condensation section liquefies and discharges the condensate, and the residual gas enters the membrane separation section;
3. The enriched gas on the membrane permeation side returns to the condensation inlet to form an internal circulation;
4. Purified gas at membrane retention side shall be discharged according to emission management requirements;
5. The recovered liquid and circulating gas volume shall be included in the operation record to observe the trend.

Comparison of single-stage and two-stage combinations

Concerns of Operation Management

Focus on whether the condensation outlet temperature falls within the set range and whether the inlet concentration of the membrane section is stable. High condensation temperature will increase the load of the membrane section and affect its service life. The performance attenuation of the membrane section usually shows a slow decline in the recovery amount, and it is necessary to judge whether to clean or replace it according to the data. Record the entry and exit parameters of the two levels as a trend, and it is clear at which level the problem occurs.

Frequently Asked Questions

Can I only do condensation without membrane separation?

Yes, but it depends on the emission requirements. Condensation is limited by the temperature level of the refrigerant, and it is difficult to meet the stricter emission management requirements when the residual concentration is too high. At this time, it is more appropriate to string the first-stage membrane separation.

Why must membrane separation be placed after condensation?

The membrane is sensitive to inlet concentration, and high concentration will aggravate pollution and load concentration, shorten life. The main body is liquefied by condensation first, and the low concentration residue is treated by the membrane section, so as to take into account the efficiency and life.

Where does the enriched gas on the permeate side of the membrane segment go?

Return to the condensation inlet to form an internal cycle, the organic components into the condensation recovery, to avoid direct discharge caused by loss.

This article by LuoyangWohong PetrochemicalEquipment Co., Ltd. arranges that the company provides design, manufacturing and operation and maintenance services for condensation recovery, membrane separation recovery and complete solvent recovery devices for chemical and pharmaceutical enterprises. If you need process evaluation or scheme configuration, please contact and exchange.